1. Field of the Invention
The invention is directed to a process and an apparatus for combustion control. More particularly, it is directed to the measurement of the potential difference between one flame of known composition and a second flame of unknown combustion in order to ascertain the oxygen activity in flames which are in over-ventilated or under-ventilated conditions.
2. Description of the Prior Art
The efficient control of combustion processes is a critical consideration in, for example, power generation, process heating, residential heating and internal combustion engines. Fast and efficient combustion control provides substantial savings in fuel consumption as well as possibly significant improvements to the air quality of exhaust generated by the aforementioned processes. One of the earliest, as well as simplest methods of combustion control consisted of accurately mixing premeasured quantities of fuel and air in order to establish and maintain a desirable air-fuel ratio. This method, however, is unreliable when controlling large burners and requires the analysis of the resulting combustion products and often the correction of the air or fuel supply to achieve the correct composition. Combustion analysis is often accomplished through the use of electrochemical sensors which deliver a voltage signal that is exponential in response. Usually, one sensor electrode is exposed to a known oxygen concentration and the other electrode is exposed to the combustion products. Additionally, the sensor must be heated to a constant or known temperature, usually above 500.degree. C. in order to obtain an accurate calculation of the unknown oxygen concentration. Because such sensors are made of zirconia ceramics, sudden heat-up can result in heat-shock destruction of the brittle ceramic and instrument failure. In a large preheat furnace, for example, the temperature upon start-up rises slowly to the level at which the ceramic sensor will function properly. Thus, for all practicable purposes, there is little or no combustion control until the sensor reaches operating temperatures.
It is an object of this invention to provide reliable and accurate combustion control which is virtually instantaneous with the start-up of combustion.
It is a further object of this invention to provide a combustion-control means which can also function as a pilot flame.
It is yet another object of this invention to provide a combustion control "reference flame" which can be used in combination with zirconia oxygen sensors.